Using recombinant DNA technology and solid phase deoxyribonucleotide synthesis, a unique hybrid gene consisting of a fragment of diptheria toxin and the sequence encoding alpha-melanocyte-stimulating hormone (MSH) has been constructed and expressed in E. coli K12. Preliminary studies of the cytotoxic properties of this novel polypeptide (MSH-toxin) on human malignant melanoma cells demonstrate that the chimeric molecule possesses characteristics intrinsic to toxin (ability to ADP-ribosylate EF-2 and block protein synthesis) and MSH (specificity for MSH-receptor bearing cells). The hybrid toxin gene product has been licensed by Seragen, Inc., which currenctly holds world-wide marketing rights. The long-range objective of this proposal is to evaluate the potential of MSH-toxin as a specific chemotherapeutic for the treatment of human malignant melanoma. Phase I of the project will (a) complete assessment of the molecule's receptor-specific cytotoxicity for human cell lines or patient material bearing MSH-receptors (b) analyze by dual beam flow cytometry, distribution of the MSH receptor as a fuction of cell cycle on in vitro and in vivo passaged melanoma cells (c) establish a human melanoma xenotransplant model in the nude mouse to characterize in vivo efficacy of primary tumor treatment with MSH-toxin. Phase II of the project will focus on (a) efficacy of MSH-toxin in a metastatic nude mouse model, (b) development of bioassay for MSH-toxin, (c) animal toxicology and investigation of MSH-toxin fate and distribution in vivo, including evaluation on impact on immune and reticuloendothelial systems.